"Share bed and board" is a phrase that refers to living together as a couple. However, there are several other ways to express this idea using synonyms. For instance, "cohabit" is often used as a more straightforward and direct term that simply means "to live together." "Roommate" is another word that can be used to describe someone with whom you share living arrangements. Additionally, "partner," "significant other," and "companion" are all commonly used terms to describe a person with whom one shares a home and other expenses. Overall, there are many ways to describe living together as a couple beyond the traditional phrase "share bed and board".